1. Introduction and chromatography
Starter…
H/W…
Summary notes – and find out about applications of gas chromatography.
What different methods of separation can you name and how do they work?
Challenge q…
Who was the 1st person to use the technique of chromatography? (not a German)
Review question maybe using a mind map on a white board

2. 5 week plan double lessons
Week 1 – Chromatography
Week 2 – Introduction to NMR
Week 3 – Structure determination / problem solving
Week 4 – TEST
Week 5 – Rates CPAC core practical
If you miss a session you MUST download the PowerPoint from the shared area and collect associated materials, this is your responsibility.
You must complete all homeworks or you will not be allowed onto Y13 chemistry. No excuses
The CPAC will be explained in more detail in your first single session with either Miss Watts or Dr Butterworth.

3. A2 chemistry topics Rates of reaction Entropy Equilibria
Further organic chemistry
Spectroscopy and chromatography
Redox chemistry / electrochemistry
Chemistry of transition metals
Arenes,
Nitrogen compounds
Synthesis

4. Warm up… CPAC 1 – Follow written instructions
Take a piece of chalk between 2
Mark a circle around the circumference of the chalk about 1 cm from one end
Check with your teacher
Place it in the sample tube with a appropriate amount of water (solvent)
Replace the lid and leave to run

5. Chromatography
Is a technique used to separate and identify the components of a mixture.
Works by allowing the molecules present in the mixture to distribute themselves between a stationary phase and a mobile phase.
Molecules that spend most of their time in the mobile phase are carried along faster.

6. Chromatography
To perform a chromatography experiment you need
Support material aka stationary phase (usually either a solid or a liquid).
Solvent aka mobile phase (usually either a liquid or a gas)

7. Chromatography Paper  TLC  Column  GC  HPLC
All use the same “partition” principle, separating mixtures of substances by their affinity between the two phases.
Substances with a greater affinity for the mobile phase will travel furthest/fastest with the solvent.

8. TLC

9. TLC
TLC
The stationary phase (often silica) is coated as a thin layer on plastic or aluminium plates.
The mobile phase (often ?) is a liquid.
The mixture is spotted on the plate and solvent is allowed to run up the plate by capillary action to separate the compounds.
Substances that are less attracted to the solid or are more soluble in the liquid move faster.
And so move further up the plate by the time that the process has been stopped by taking the plate out of the liquid. - larger Rf

10. Can TLC be used for colourless compounds?
Compare mixtures in sample with known substances

11. Retention factor
…is a measure of how far it has moved up a plate under certain conditions
it is can be use a quick way of identification.
Differences in Retention Factors are important when considering solvent systems for Column Chromatography.

12. Retention factor Rf = distance moved by substance
distance moved by solvent front
For substances that are very soluble in the liquid Rf will be close to ....
For substances that are rather insoluble in the liquid Rf will be close to ....

13. Column Chromatography
The stationary phase in placed in a column and the solvent is allowed to move the mixtures through whilst collecting fractions of the emerging solvent.
Separation by column chromatography depends on the balance between solubility in the moving phase and retention in the stationary phase.
This can be carried out by allowing the solvent to flow under gravity or under a moderate pressure to increase the solvent flow rate
The fractions are usually analysed by TLC in order to identify which contain the components of the mixture.

14. Column Chromatography

15. The Column is contained in a thermostatic oven.
Gas Chromatography
Injection
port
Recorder
Oven
Detector
Column
The Column is contained in a thermostatic oven.
(Why ?)
Nitrogen
cylinder

16. Gas Chromatography GC
About 1μL of liquid is injected into one end of the column.
The Retention Time is characteristic of a particular substance. (for the same column, temperature, gas flow etc.)
As each component reaches the other end it is detected and registered on a chart recorder.
The area under each peak indicates the relative quantities.

17. Factors affecting retention time:
Gas Chromatography
flow rate of carrier gas
length of column
Factors affecting retention time:
temperature of column.
packing material
type of carrier gas

18. Gas Chromatography Uses of GC
Very sensitive - small quantities of substances detected, explosives, drugs etc.
Separation of pure substances for collection.
Uses of GC
Can be connected to mass spectrometer for direct identification of substances.

19. Gas Chromatography
Suggest identities of some of the unlabelled peaks.

20. Column chromatography
Your turn
Gas chromatography
Food dye – paper
Food dye - TLC
HPLC
Column chromatography

21. Paper chromatography Equipment capillary tubes
food dye samples (made up in EtOH)
solvent bottles A = H2O, B = 50:50 H2O : EtOH C = 100% EtOH
Chromatography paper
Beaker
Watch glass
What you need to do
Test the food dye samples using three different solvents to determine which solvent is most suitable. You are looking for the solvent that gives the best separation.

22. TLC Equipment Food dyes made up in EtOH TLC plates 50:50 EtOH : H2O
Beaker
Watch glass
What you need to do
Test the food dye sample using a solvent to determine whether the TLC plate gives a better separation than the paper chromartography

23. Column chromatography
Equipment
Mini columns
Cotton wool
Alumina / silica
Nichrome wire pokey sticks
Clamp stands
Solvent mix 50:50 MeOH: EtOH
Berol black ink
Plastic pipette
What you need to do
Pack the columns using a cotton plug and either alumina or silica. Place a few drops of the ink in the top of the column and allow the mixture to separate

24. Gas chromatography Equipment U-tube packed Syringe Hydrocarbon mixture
Reference flame
Water bath
Methane carrier gas
What you need to do
Inject a sample of the volatile hydrocarbons into the rubber septum and watch the flame. Compare it to the reference flame to determine when the fractions of the mixture have travelled through.

25. HPLC - Video

26. How does HPLC work?

27. Plenary 1 Paper / Silica gel on plastic film Paper / TLC Inert gas
High boiling point liquid on inert solid support
Organic or aqueous solvent
HPLC
Organic or aqueous solvent
Silica gel GC

28. Plenary 2
What is the difference between chromatography and spectroscopy?
What key words would you use when describing how chromatography works?
What types of chromatography can you now name?
What are the key differences and similarities between HPLC and GC?

30. Useful references
Link 1
Link 2